I. Field
The following description relates generally to wireless communications, and more particularly to providing feedback related to resource utilization of an access terminal that can be leveraged for downlink flow control in a Long Term Evolution (LTE) based wireless communication system.
II. Background
Wireless communication systems are widely deployed to provide various types of communication; for instance, voice and/or data can be provided via such wireless communication systems. A typical wireless communication system, or network, can provide multiple users access to one or more shared resources (e.g., bandwidth, transmit power, . . . ). For instance, a system can use a variety of multiple access techniques such as Frequency Division Multiplexing (FDM), Time Division Multiplexing (TDM), Code Division Multiplexing (CDM), Orthogonal Frequency Division Multiplexing (OFDM), and others.
Generally, wireless multiple-access communication systems can simultaneously support communication for multiple access terminals. Each access terminal can communicate with one or more base stations via transmissions on forward and reverse links. The forward link (or downlink) refers to the communication link from base stations to access terminals, and the reverse link (or uplink) refers to the communication link from access terminals to base stations. This communication link can be established via a single-in-single-out, multiple-in-single-out or a multiple-in-multiple-out (MIMO) system.
MIMO systems commonly employ multiple (NT) transmit antennas and multiple (NR) receive antennas for data transmission. A MIMO channel formed by the NT transmit and NR receive antennas can be decomposed into NS independent channels, which can be referred to as spatial channels, where NS≦{NT, NR}. Each of the NS independent channels corresponds to a dimension. Moreover, MIMO systems can provide improved performance (e.g., increased spectral efficiency, higher throughput and/or greater reliability) if the additional dimensionalities created by the multiple transmit and receive antennas are utilized.
MIMO systems can support various duplexing techniques to divide forward and reverse link communications over a common physical medium. For instance, frequency division duplex (FDD) systems can utilize disparate frequency regions for forward and reverse link communications. Further, in time division duplex (TDD) systems, forward and reverse link communications can employ a common frequency region so that the reciprocity principle allows estimation of the forward link channel from reverse link channel.
Wireless communication systems oftentimes employ one or more base stations that provide a coverage area. A typical base station can transmit multiple data streams for broadcast, multicast and/or unicast services, wherein a data stream may be a stream of data that can be of independent reception interest to an access terminal. An access terminal within the coverage area of such base station can be employed to receive one, more than one, or all the data streams carried by the composite stream. Likewise, an access terminal can transmit data to the base station or another access terminal.
Access terminals typically support multimedia and many different applications running concurrently (e.g., email, voice, video, . . . ). Long Term Evolution (LTE) based environments can also enable supporting very high data rates (e.g., data can be sent over the downlink at rates on the order of 100 Mbit/s, 300 Mbit/s, . . . ). Further, each application can demand a certain amount of resources from the access terminal (e.g., processing power, buffers, battery power, . . . ). Moreover, the amount of resources needed at a given time can be dynamic.
It is to be appreciated that access terminals can be designed to handle the sum of maximum instantaneous requirements of all applications that can be effectuated therewith. To maintain costs associated with access terminals at a reasonable level, however, access terminals can be designed to handle common load conditions rather than peak instantaneous requirements, which can be significantly larger than the common load. For example, the peak instantaneous requirements can occur when all applications supported by an access terminal happen to launch concurrently while the access terminal is simultaneously receiving data at the peak rate via the downlink. Thus, the access terminal can be provisioned to handle the peak rate for a short duration of time rather than being able to sustain operability at the peak rate for an extended period of time, which in turn can significantly reduce costs associated with the access terminal.
If an access terminal is not over-dimensioned (e.g., designed to accommodate common load conditions rather than peak instantaneous requirements for an extended period of time, . . . ), it can run low in resources. When availability of resources of an access terminal is low, the access terminal can attempt to reduce its load. However, LTE currently fails to support providing feedback from the access terminal to the base station when the access terminal is experiencing low resources. For example, if the base station is sending data to the access terminal at a high speed (e.g., 100 Mbit/s, . . . ) for an extended period of time, the access terminal can be unable to handle processing of such downlink data and/or the buffer can become full; meanwhile, the access terminal can lack a manner by which it can notify the base station to reduce the downlink transmission rate.
In UMTS Terrestrial Radio Access Network (UTRAN), flow control is supported in Radio Link Control (RLC). According to an illustration, an access terminal operating in UTRAN can set a transmitting window size of a base station for flow control purposes; thus, when the access terminal is congested, the access terminal can collapse the transmitting window size of the base station. The aforementioned flow control technique utilized in UTRAN, however, is not applicable to LTE since the RLC has been redefined in LTE. Accordingly, utilization of the RLC for flow control is inoperable in LTE.